Choe, who took the job in June 2014, was executed by firing squad in May after voicing opposition to forestry policies promoted by Kim, the agency said, citing the source 'with knowledge of the North'.

Choe was last seen in the North's state media last December at the death anniversary of the late leader Kim Jong-Il, South Korea's unification ministry said today. “Seoul was closely monitoring the possibility of any changes in Choe's circumstances", said the ministry, which is in charge of cross-border affairs.

Choe's death, if confirmed, would be the second reported this year. Defence minister Hyon Yong-Chol was said to have been executed in April by anti-aircraft fire for insubordination and dozing off during formal military rallies.

Such a violent method of execution has been cited in various unconfirmed reports as being reserved for senior officials who the leadership wished to make examples of. The North has not officially confirmed Hyon's execution -- reported in May by Seoul's intelligence agency – but announced his replacement, Pak Yong Sik, in July.